The application can then perform any tidy up operations necessary to ensure what is on disk is consistent. The snapshot starts and the applications are then notified they can continue.
Now the on disk state should be fine. When do I need to check my applications are VSS aware? You need VSS writers for applications that perform large amounts of IO and depend heavily on the state of the files they are writing if you wish to back them up. Most applications do not write to disk in quantities of data large enough to be a problem.
Many applications from Microsoft are also VSS aware, which helps greatly. VSS is smart enough to keep track of its temporary storage location, and will exclude anything in it, including the current temporary storage area and any persistent snapshots that have been previously created. So when the data is read by your backup software, you only get what you need. Well, VSS solves the problem of imaging a live system neatly, so whenever you image your system with Reflect you are probably using VSS.
Reflect can use this on these systems if VSS is unavailable. Why have both systems? We know it will be there as Microsoft are committed to this feature and it makes sense to use it as it is highly reliable.
Before VSS we had no such mechanism so we built our own. It is equally as reliable but we felt the feature additions of VSS and the support for writers for enterprise scenarios really meant VSS made sense. However in the rescue environment we do not use, or need to use, either pssnap. Because the system is not in use so the data should be perfectly consistent at all times. Of course we may well end up including persistent snapshots if they exist because without VSS they are not excluded.
The VSS requestor announces that it needs to create a server snapshot. Before it creates the snapshot, it queries the server to determine which VSS writers have been installed so it can instruct the writer to disable its backup application. The VSS requestor will instruct each writer to accomplish pre-backup tasks needed for data quiescence.
After those tasks are completed, the requestor instructs the VSS provider to create a snapshot. The provider tells the requestor where to locate the data it needs, and then the backup process begins.
When the backup is complete, the VSS requestor announces it has completed all the activities, and it instructs each VSS writer to perform any post-backup tasks necessary, so the computer and its applications can return to normal operation. This means that they can clear their transaction logs and perform other maintenance tasks.
Instead of using a traditional backup agent, such as with Exchange, the backup app with VSS can tell Exchange to quiesce itself. Provider — This component provides the VSS service by creating and maintaining shadow copies. It guarantees that you have a consistent data set to back up.
Check the Event Logs Application and System are common. Determine if any VSS writers have failed. Review the Task Scheduler for jobs that may be running when the backup application runs. Check that the schedules for SQL Maintenance and Exchange Maintenance plans do not conflict with the schedules for the backup application.
Schedule a demo today! About the Author: Naj Raza. Related Posts. The system provider can expose the production volume, which can be written to and read from normally. When the shadow copy is needed, it logically applies the differences to data on the production volume to expose the complete shadow copy. For the system provider, the shadow copy storage area must be on an NTFS volume. The Windows operating system includes a set of VSS writers that are responsible for enumerating the data that is required by various Windows features.
In addition to backing up application data and system state information, shadow copies can be used for a number of purposes, including the following:. This is a fast-recovery scheme that allows an application administrator to restore data from a shadow copy to the original LUN or to a new LUN. The shadow copy can be a full clone or a differential shadow copy. In either case, at the end of the resync operation, the destination LUN will have the same contents as the shadow copy LUN.
During the resync operation, the array performs a block-level copy from the shadow copy to the destination LUN.
While the resync operation is in progress, read requests are redirected to the shadow copy LUN, and write requests to the destination LUN. This allows arrays to recover very large data sets and resume normal operations in several seconds. In a LUN swap, the shadow copy is imported and then converted into a read-write volume. In LUN resynchronization, the shadow copy is not altered, so it can be used several times.
In LUN swapping, the shadow copy can be used only once for a recovery. For the most safety-conscious administrators, this is important. When LUN resynchronization is used, the requester can retry the entire restore operation if something goes wrong the first time. For this reason, the shadow copy LUN must use the same quality of storage as the original production LUN to ensure that performance is not impacted after the recovery operation. If LUN resynchronization is used instead, the hardware provider can maintain the shadow copy on storage that is less expensive than production-quality storage.
All of the operations listed are LUN-level operations. If you attempt to recover a specific volume by using LUN resynchronization, you are unwittingly going to revert all the other volumes that are sharing the LUN. Shadow Copies for Shared Folders uses the Volume Shadow Copy Service to provide point-in-time copies of files that are located on a shared network resource, such as a file server.
With Shadow Copies for Shared Folders, users can quickly recover deleted or changed files that are stored on the network. Because they can do so without administrator assistance, Shadow Copies for Shared Folders can increase productivity and reduce administrative costs. With a hardware provider that is designed for use with the Volume Shadow Copy Service, you can create transportable shadow copies that can be imported onto servers within the same subsystem for example, a SAN.
These shadow copies can be used to seed a production or test installation with read-only data for data mining.
With the Volume Shadow Copy Service and a storage array with a hardware provider that is designed for use with the Volume Shadow Copy Service, it is possible to create a shadow copy of the source data volume on one server, and then import the shadow copy onto another server or back to the same server.
This process is accomplished in a few minutes, regardless of the size of the data. The transport process is accomplished through a series of steps that use a shadow copy requester a storage-management application that supports transportable shadow copies. Import the shadow copy to a server that is connected to the SAN you can import to a different server or the same server.
A transportable shadow copy that is created on Windows Server cannot be imported onto a server that is running Windows Server or Windows Server R2.
A transportable shadow copy that was created on Windows Server or Windows Server R2 cannot be imported onto a server that is running Windows Server However, a shadow copy that is created on Windows Server can be imported onto a server that is running Windows Server R2 and vice versa.
Shadow copies are read-only. It works only if there is a hardware provider on the storage array. Shadow copy transport can be used for a number of purposes, including tape backups, data mining, and testing. In the case of a hard disk drive backup, the shadow copy created is also the backup. Data can be copied off the shadow copy for a restore or the shadow copy can be used for a fast recovery scenario—for example, LUN resynchronization or LUN swapping. When data is copied from the shadow copy to tape or other removable media, the content that is stored on the media constitutes the backup.
The shadow copy itself can be deleted after the data is copied from it. It depends on the backup software that you used. Most backup programs support this scenario for data but not for system state backups. It depends on the backup software you used. If you create a shadow copy on Windows Server , you cannot use it on Windows Server
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